Boron binding plant growth agents

ABSTRACT

Herbicidal compositions including a benzazaboroxane precursor such as an aryl substituted N,N&#39;&#39;-bis-(hydroxyalkyl)-2hydroxybenzylamine compound are disclosed. Increased herbicidal activity is observed with increasing oil solubility of the compound. Activity appears to proceed by binding or mining boron from the plant due to the ligand action of the compounds in forming benzazaboroxanes.

United States Patent Swidler et al.

[451 Nov. 19, 1974 1 BORON BINDING PLANT GROWTH AGENTS [75] Inventors: Ronald Swidler; Harris M. Benedict,

both of Pasadena, Calif.

[73] Assignee: Stanford Research Institute, Menlo Park, Calif.

22 Filed: Ju1y23, 1971 21 App1.No.'. 165,750

[52] US. Cl 71/76, 47/12, 71/66,

71/121 [51] Int. Cl. A01n [58] Field of Search 71/121, 76

[56] References Cited UNITED STATES PATENTS 3,047,609 7/1962 Swidler 260/462 R 3,181,942 5/1965 Popoff 71/121 3,271,435 9/1966 Randall et al 71/121 Primary Examiner-James 0. Thomas, Jr. Attorney, Agent, or Firm-Lindenberg, Freilich, Wasserman, Rosen & Fernandez;

[ 5 7] ABSTRACT 7 Claims, No Drawings 1 2 BORON BINDING PLANT GROWTH AGENTS where R; is hydrogen or lower alkyl of l-l carbon l 1 BACKGROUND OF THE INVENTION atoms, R is methylene cthy ene or 1 1. Field of the Invention GHPCQ The present invention relates to plant growth control 5 u and more Particularly to boron binding Plant growth group, R, is hydrogen, hydroxyl or alkyl, and R is hycontrolling agents. drogen, hydroxyl, halogen, an alkyl group, aryl, halo- 2' Description of the Prior Art aryl, alkoxy, haloalkyl, carboxyl. a p-hydroxydimethylbenzyl group and R, and R when joined together and taken with the benzene from a naphthalene group. The aryl groups may be selected from phenyl, biphcnyl, tolyl and xylyl. Useful halogens include chlorine, bromine or iodine. The R, and R allkyl groups preferably contain at least 6 and usually not more than 20 carbon atoms.

The precursors are conveniently prepared by solvolysis of the corresponding benzazaboroxane of the for- It is known that the presence of boron at low levels I is essential for metabolism and normal growth of certain plants and that at higher levels boron is toxic to these plants. Chelating agents have been added to high boron content irrigation water to bind the boron and reduce the toxic action on plants. However, these agents have not been found to be very effective in rendering boron nontoxic to sensitive agricultural crops.

A class of exceptionally water stable organic borate i l esters are disclosed in US. Pat. No. 3,047,609. Simple alkyl borates or aryl borates spontaneously hydrolyze R 14 H in water. However, the benzazaboroxane esters disclosed in the cited patent can be formed directly from H the addends by reaction in aqueous media.

3 SUMMARY OF THE INVENTION 3 B The present invention relates to the use of precursors 0 of these borate esters as plant growth controlling V agents. The precursors arecornpounds o f thefo r n ulaez; 2 (III) and where R, R R and R have the previously defined CF R OH meanings. A series of N,N'-bis-(fi hydroxyethyl)-2- "2 3 hydroxybenzylamine ligands were prepared from 3- CH R OH substituted-benz-(7,8)-l-aza-5-boro-4,6,l3-trioxa- 2 3 5O bicyclo-(4,3,3)-dodecanes according to the following procedure. The dodecanes were synthesized via amodified Mannich reaction as described in US. Pat. No. 3,047,609, the disclosure of which is incorporated R herein by reference. 7

EXAMPLE 1 A suspension of about 1.5 mol of the benzazaborox- R ane in 500. cc of methanol was saturated with dry by- I C drogen chloride whereupon the benzazaboroxane dissolved. The solution was placed on a steam bath and 3 the methanolmethyl borate azeotrope (bp 54.6C, HOR CH2 75.5% methyl borate) was removed by distillation. The

3 CH residual methanol was removed in vacuo and the crys- OR CH I talline residue was recrystallized from isopropanol or R ethanol. After the second recrystallization white powdery crystals were obtained. The precursor compounds 0H (II) have the following structural formula:

and OH CH CH CH OH T he firac teristics of the S-R-substituted-N,N'-bis In the absence of excess boron, the TIPA chelating agent and the carboxy substituted ligand compound did not exhibit phytotoxicity. No injury to the plant was noted and possibly some increase in growth was evidenced. The chloroand the lower alkyl butyl substituted ligands depress the dry weight of the plant somewhat to afford a low level of phytotoxicity. The ligand agents which had two benzene rings and the higher alkyl octyl substituted ligand compound were extremely toxic. Toxicity symptoms developed within 16 hours and within 2 days almost all the leaves had (B-hydroxyethyl)-2-hydroxybenzylamine hydrochlodropped off. These plants made little or no growth durrides are provided in the following table. ing the experimental period of 2V2 months.

TABLE 1 Borate Ester Melting Shortened Melting Point N0. R. R Name Point C pK* NE" MW "C I H H Basic 246.6 224- 2 Carboxy H Carboxy 172-3 5.6 275.5 275.5 328 3 Chloro H Chloro 142.6 6.2 269.1 269.l 240-1 4 Naphtha (RI+R2) Naphtha 127-32 6.4 305 297.8 297 8 5 t-Butyl H Butyl 157-60 6.5 272.3 303.8 2978 6 Biphenyl H Biphenyl 7 lsooctyl octyl H 146-7 6.6 347.0 359.9 204-6 The borate esters readily reform directly from the addends by reaction in aqueous media. Experiments have demonstrated that the reaction proceeds at low concentration (equivalent to 10 ppm B) to an equilibrium state containing up to 90% of the tryptych structured benzazaboroxane esters.

To ascertain the biological activity of the boron binding ligands of the invention, five replications of Black Valentine bean plants were grown in water culture consisting of complete nutrient solutions absent boron and containing 10 ppm excess boron as sodium borate. The ligands were added to the nutrient solution in an amount equivalent to 10 ppm of boron. Additionally, a control solution absent a ligand was prepared and a solution containing triisopropylamine (TIPA) a known boron binding chelate was prepared. The results of the dry weight determinations are described in the following table.

TABLE 2 BORON CONTENT DRY WEIGHT-GRAMS il/kt:

NO 10 PPM NO I0 PPM PLANT PART AND EXCESS EXCESS EXCESS EXCESS CHELATING BORON BORON BORON BORON AGENT Tops None 5.40 2.12 I0 308 'IIPA 5.68 3.26 10 235 ('arboxy 6.]8 3.00 8 2l3 ('hloro 4.75 2.58 l I 303 Nuphthn 0.76 .l6, I6 580 Butyl 3.75 2.58 I2 288 Bi Phcnyl 0.74 .60 I4 455 ()etyl Died Died Roots None .50 .22 24 I86 TIPA .60 .40 21 I02 Curhoxy .96 .48 I4 I29 (hloro .64 .50 I4 I80 Naphtha .44 .l2 I8 57 Butyl .76 .66 I2 I62 Bi Phenyl .16 .32 l I 67 ()ctyl Died Died The plants growing in the 50111065510 which I0 ppm of boron alone was added developed typical boron toxicity symptoms in a few days. The addition of a chelating agent of ligand compound to the boron in the solution did not delay the appearance of the symptoms although the severity was less with some plants. This was reflected in the dry weight of the tops of the plants. Again, the TIPA chelating agent and the carboxy substituted ligand compound did not injure the plants but g sa fit m d nqsa i s ewthh li and 9 pounds containing 2 benzene rings and the higher alkyl octyl substituted compounds were again extremely toxic in themselves.

The ligand agents do afford the plants some, but not complete protection against excess boron with the exception of naphtha and octyl. It is apparent that the ligand agents are effective plant growth regulating substances to reduce boron toxicity effects of plants in the presence of high boron irrigation sources. Selected Iigands in normal low boron irrigation waters and soils are effective as plant dwarfing or phytotoxic herbicidal agents.

When no born was present in the nutrient solution the boron contents of the plants did not differ significantly whether the chelating or ligand agents were present or not. In the presence of excess boron, boron toxicity symptoms on sensitive crops are reduced even though the plants take up an amount of boron 10 to 20 times that normally taken up. Therefore, boron appears to be uniquely unavailable to metabolizing the plants. It is also noted that the naphthyl, biphenyl and octyl ligands appear to induce the highest immobilization of boron into the plant substrates.

In order to further verify the biological action of the ligands, a group of the corresponding tryptych benzazaboroxane esters were selected for addition to a standard plant nutrient solution and vegetative response was observed in both sand and water culture. A control and an equivalent boro'n containing medium (boron as sodium borate) were included in the randomassumed that transference of the boron proceeds ized screening experiments. Appropriate boron analy through reaction into an oil-phase in the plant, one sis was performed at intervals and at the termination of g t expect a Shift in the equilibrium boron content the experiments, The dry weights and boron contents VlS-a-VlS nutrient medium, plant aqueous sap and plant of the Black Valentine bean plants are summarized in lipid g rh f ll i t bl The phytotoxic N,N'-bis-(hydroxyalkyl)-2- TABLE 3 Plant Boron Content Boron Content of Nutrient Solution Per Unit Weight and Ligand Chelating Dry Weight Per Plant Mg/Kg Dry Weight Agent Tops-Grams Roots-Grams Mg/Kg Mg/Kg Beans Sodium Borate 0.80 0.38 US 40 Basic Ester 2.92 1.18 285 82 Carboxy Ester 3.l4 .88 61 55 Control-No excess boron 3.78 1.24 12 5 The control solution contained 0.! ppm of boron to supply boron requirements, other solutions. therefore, contained 10.1 ppm. 2 L.S.D. Least Significant Difference Though lethal quantities of boron appeared in all the; hydroxybenzylamine agents according to the invention plants exposed to the borate esters, there was only a can be applied to the nutrient or irrigation water for the yery moderate dimmunition in plant vigor as compared 5 plant, or can be applied directly to the plant as an aqueto tFie etSrTt rETwhereasSoHi um borate at the same level I 2 ous spray solution or in adry powdered form mixed of boron was extremely toxic to the plants. with various inert carriers. Under normal soil and irri- Since the preformed borate ester is not toxic to the gation conditions, where the boron content of the plant, whereas the ligand when administered alone to Water is at a level of pp 8 Concentration 0f IOTS the plant exhibits a high level of phytotoxicity it is bemols P liter of the ligand agent is Capable of Plant lieved that the biological action is due to the ligand. growth Control as dwarflhg ageht; At a cohcehtratloh binding boron f the plant and inducing a Severe of at least 10" mols per liter, the ligand agents exhibit boron deficiency in the plant. Thus, the ligands can be Phytotoxlc QCUOIL e Concentrat on should be inappried to the plant at lower Concentrations to induce creased for high boron containing 50115 or irrigation waminor element deficiencies as a useful dwarfing agent I or at higher concentration levels as a phytotoxic herbi- It 15 to be understood that y Preferred embodl id ments of the invention have been described and that On th basi of lti i t d other h i l numerous substitutions, modifications and alterations considerations and an estimation of the partition coeffiare all permissible without departing from the spirit and cient'of selected ligands, it was postulated that phyto- 4O scope of the invention as defined in the following toxic action would be more apparent for those comclaims. pounds exhibiting a highly favorable oil-to-water solu- What is claimed is: bility. The more likely it appeared that the borate water 1. A method of dwarfing the growth of plants comwould tend to partition into an organic solvent or oil i i th Stop f l i t h l t an ff iv Phase, the more toxic the Compoundsamount of a compound of the formulae:

It was determined that the ratio of concentrations of the basic compound in an organic solvent over water OH was 0.23 but the ratio of concentration of the borate ester was over 200 probably between 500 and 1000. HOR -CH f Therefore, phytotoxic herbicidal compositions in acso N-CH cordance with the invention preferably include a ligand 0 Ht'JR -CH compound in which either R or R is a substituent that g OH provides an oil partition coefficient of at least 0.23, 2 3

suitably being selected from naphtha, phenyl or higher a CH 01- alkyl containing 6 to 20 carbon atoms. R 2 3 The higher toxic action of the more oil soluble com- 0H pounds is further biologically interesting since these materials were supplied to the plants from aqueous meand dium. Therefore, consideration of translocation through the waxy epidermal leaf layers does not seem O CHZRQOH germane. Moreover, since substitution of the benzene ring in these ligands does not effect their base strengths 0112123011 appreciably, it can be concluded that the boron binding ability remains relatively unchanged. This again ampli- R2 fies the role of partition in the biological action. Fi-

nally, it is interesting that the more oil soluble ligands, where R, is selected from hydrogen and lower alkyl of naphtha, phenyl and octyl, appear to induce the highest 1 to 10 carbon atoms; R is selected from methylene,

mntq za iq tq QQLQU hsptantsubstrate .ltitis ethylene and "if imiiiliti aEeBRiiHg t R is selected from hydrogen, hydroxyl, halogen. alkyl, aryl, haloaryl, alkoxy, haloalkyl, carboxyl and p-hydroxydimethylbenzyl; R is selected from hydrogen, hydroxyl and alkyl and R and R when joined together and taken with the benzene ring form naphthalene.

E ciai iii i in which th'caapound is a N,N-bis-(Bhydroxylalkyl)-2- hydroxybenzylamine of formula I where at least one of R and R ai'si'idtrm hydrogen, phenyl, naph I thyl, alkyl of 62() carbon atoms and haloalkyl of 6-20 carbon atoms. 

1. A METHOD OFF DWARFING THE GROWTH OF PLANTS COMPRISING THE STEP OFF APPLYING TO THE PLANTS AN EFFECTIVE AMOUNT OF A COMPOUND OF THE FORMULAE:
 2. A method according to claim 1 in which the compound is a N, N''-bis-( Beta -hydroxylalkyl)-2-hydroxybenzylamine of formula I where at least one of R1 and R2 are selected from hydrogen, phenyl, naphthyl, alkyl of 6-20 carbon atoms and haloalkyl of 6-20 carbon atoms.
 3. A method according to claim 2 in which R3 is methylene.
 4. A method according to claim 3 in which R2 is octyl.
 5. A method according to claim 1 in which the compound is applied to the plant as an aqueous solution.
 6. A method according to claim 5 in which the solution is applied to the soil in which the plant is growing.
 7. A method according to claim 6 in which the compound is present in the solution in an amount at least 10 3 molar. 